This non-provisional application claims priority under 35 U.S.C. § 119(a) to Korean Patent Application No. 2003-83584 filed on Nov. 24, 2003, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an organic thin film transistor comprising a buffer layer, and more particularly to an organic thin film transistor comprising a substrate, a gate electrode, a gate insulating layer, an organic semiconductor layer, source-drain electrodes and a protective layer. A buffer layer is interposed between the organic semiconductor layer and the protective layer, thereby minimizing the deterioration in the performance of the transistor caused by ambient air containing oxygen and moisture, and mounting process of a display device thereto.
2. Description of the Related Art
Recently, polymers have been actively investigated as novel electrical and electronic materials in a wide variety of applications (e.g., functional electronic and optical devices). The investigations have focused on easy molding into the form of fibers and films, high flexibility, high conductivity and low manufacturing costs. Among devices fabricated from these conductive polymers, research on organic thin film transistors fabricated using organic materials as semiconductor layers has been conducted since the 1980's. In this connection, a number of studies are now being actively undertaken around the world. Organic thin film transistors are expected to be useful for driving devices of active displays and in plastic chips for use in smart cards and inventory tags. A device using an organic thin film transistor necessitates a protective layer for protecting the transistor from ambient air containing oxygen and moisture, and a supporting layer for mounting a display device, particularly in the case of a display application. There are currently no effective techniques for forming a protective layer or supporting layer in organic thin film transistors. Some attempts to form an inorganic film made of SiNx, SiOx, etc. on an organic thin film transistor by CVD or sputtering have been made, but the processes cause serious deterioration of the organic semiconductor layer due to active gases or plasma. This results in drastic reduction in the performance of the organic thin film transistor.
Several methods using an organic film made of a polyimide, BCB (benzocyclobutene) or photoacryl as a protective layer have been performed. However, these methods are not effective in forming a protective layer of an organic thin film transistor in that the organic active layer is drastically deteriorated at an annealing temperature higher than 150° C. The major problem caused in the film formation of a protective layer using an organic material is the direct contact between a material used to form the protective layer and an organic semiconductor layer. At this time, an organic solvent used in the formation of the protective layer deteriorates the performance of the organic semiconductor layer. Jackson, a professor at Penn. State University and his team tried to effectively form a protective layer using an organic film of PVA (polyvinyl alcohol). However, this method which used patterned pentacene as an organic semiconductor layer, has a problem in that the charge carrier mobility is decreased to ⅓ of its initial value after processing (Solid-State Electronics 47(2003) 297–301).
No approaches that can avoid a decrease in the performance of an organic thin film transistor caused upon forming an organic or inorganic film as a protective layer have been reported until now. Accordingly, development of novel protective layers and processes effective for forming the protective layers is necessitated to manufacture applied products using organic thin film transistors.